Filter members frequently are used on terminals and in electrical connectors to reduce noise and in particular to reduce electromagnetic interference (EMI) an radio frequency interference (RFI). EMI is electromagnetic energy whether it occurs naturally or man made and causes undesirable responses, malfunctions and/or complete failures in electrical equipment. It is often desirable, therefore, to use filters to suppress any external EMI from entering equipment or to absorb or suppress any EMI from being generated by the equipment. RFI is now used interchangeably with the term EMI but generally is limited to interference in the radio communication band.
Filter members are generally comprised of a core material with a layer of plating disposed thereon to form terminal electrodes and ground electrodes. The core member may be comprised of one or more layers to form a sleeve for individual terminals or may be layered in a flat arrangement to form a planar filter member for a multitude of electrical terminals. The core material may be made from a variety of material as is known in the art.
It is important in constructing the filter that the electrical terminal electrodes and the ground electrodes be isolated from each other. Typically this is accomplished by the use of a plating resist, which is applied to the desired surface areas of the core, prior to plating. Plating material is then deposited on the uncoated surfaces to define terminal and ground electrodes, the electrodes being isolated from each other by the plating resist. Generally the plating resist had to be removed prior to soldering the filter members to electrical terminals because conventional plating resists cannot withstand the temperatures and chemicals associated with soldering procedures.
Another way to achieve electrical isolation of the terminal and ground electrodes is to coat the entire core material with the plating material and then selectively remove some of the plated layer by grinding or other such means to chamfer the ends and isolate the terminal electrode from the ground electrode.
One disadvantage in either of the procedures described above, is that one or more additional handling and manufacturing procedures must be performed to the plated filter member before it is ready for electrical engagement with a terminal member.
The exposed surface of the core remaining after either of the aforementioned processes must be protected from the environment during use, particularly from moisture, cleaning solvents, and the like. In many instances the filter members, such as sleeves or planar members are used in an electrical connector which is potted. This potting material covers essentially the whole sleeve, which includes the exposed surfaces of the core thus protecting them from damage owing to moisture, cleaning solvents or the like. In those instances where the electrical connectors are not potted or the filters are being used as loose piece filters or filtered terminals, other means, such as coating the exposed core surfaces with an epoxy or other sealant, have also been used.
It is an object of the present invention to provide a sealed filter member which may be used in potted connectors or as a loose piece filter member.
Furthermore, it is an object of the invention to provide a filter member having a dielectric material disposed on an unplated filter member to define and electrically isolate pin and ground electrode means on the filter surface, said material also providing a plating resist and permanently sealing the body means at those portions.
It is an additional object of the invention to provide means for sealing such filters that is cost effective and usable in automated manufacturing systems.
It is also an object of the invention to provide a means for manufacturing sealed filters that requires a minimum number of manufacturing procedures.
It is an additional object of the invention to provide a means for making sealed filter members that minimizes handling of the filter members.
It is also an object of the invention to provide a plating resist that will also provide protection from solder.
Another object of the invention is to provide a dielectric polymerizable material that can be polymerized on an unplated filter means to form plating resist, solder resist and seal for the surfaces of the filter so coated.